Method of removing paraffin from a well with heated solvent



United States Patent "ice US. Cl. 166-303 8 Claims ABSTRACT OF THEDISCLOSURE A method of removing paraffin deposits from a producing wellincluding injecting heated xylene bottoms solvent into the well bore ata temperature sufiiciently high so that the solvent is at least 150 F.when it encounters the producing formation and thereafter pumping fromthe well to remove the solvent and dissolved paraffin and the solventtherefor which includes reformed aliphatic aromatic hydrocarbons and astabilizing catalyst additive which functions to accelerate thedissolving of paraffin deposits and to increase the capacity of thesolvent to retain the parafiin in solution when the solvent is cooled tothe temperature of the producing formation.

Background of the invention Many oil and gas wells, particularly pumpingoil wells, are subject to greatly reduced production resulting fromparafiin deposits on the producing. formation in the vicinity of thewell bore. Hot water, steam and a great variety of solvents have beeninjected into the well bores in an effort to remove the depositedparaffin and thereby regain some of the lost production capacity. Whilesome success has been achieved in increasing production, the increasedproduction has not been sufiicient in relation to the expense of thetreatment to render any of such treatment successful.

Summary The present invention relates to an improved paraffin solventand an improved method of removing paraffin from a producing formation.

It is therefore, an object of the present invention to provide animproved method of removing paraffin from a well which results in verysubstantial increased production from the well.

Another object is to provide an improved method of removing paraffinfrom the face and immediately surrounding producing formation in a wellbore to increase the recovery from said producing formation at arelatively low cost in relation to the amount of the increase inproduction from the treated well.

These and other objects and advantages of the present invention arehereinafter set forth and described in detail.

THE PREFERRED EMBODIMENTS The solvent 3,437,146 Patented Apr. 8, 1969 Atypical solvent of the present invention for use in treating atproducing well includes 4,200 gallons of xylene bottoms having a boilingpoint of 308 F. together with gallons of a stabilizing catalyst additivehaving the following composition:

Component: Approximate percent by weight Carbon bisulfide 30 Naphthalene22 An oil soluble surface active agent 12 A Water soluble surface activeagent 10 A combined oil and water soluble surface active agent 13Terpene hydrocarbons 5 Kerosene 8 An oil soluble surface active agentwhich has been found to be particularly effective in such additive iscommonly described as sorbitan partial fatty esters and is a mixture ofesters of sorbic alcohol and oleic, palmitic and stearic acids. Such aproduct is sold by Atlas Powder Company under the name Atpec-ZOO. Thefunctions of this agent is to reduce the surface tension of thehydrocarbon fluids encountered by the solvent to thereby assure readyaccess of the solvent to the parafiin deposits to be dissolved. Theparticular agent has a specific gravity of 1.000, a viscosity of 1000cp. 25 C., an HLB (hydrophilic-lypophilic balance) of 4.3 and isnonionic.

A water soluble surface active agent which has been found to beparticularly effective is polyoxyethylene alkyl aryl other which is aneight mol ethylene oxide adduct of nonyl. phenol and is nonionic. Such aproduct is sold by Atlas Powder Company under the name Renex 648. Thefunction of this agent is to reduce the surface tension of the water andbrine encountered by the solvent in the producing formation to therebyassure ready access of the solvent to the paraflin to be dissolved. Theparticular agent has a specific gravity of 1.030, a viscosity of 223 cp.25 C. and an HLB of 10.3.

A combined oil and water soluble surface active agent which has beenfound to be particularly effective is an alkyl phenol ethylene oxidecondensate. Such agent is a ten mol ethylene oxide adduct of nonylphenol and is nonionic. Such agent is sold by Chevron Oil Company underthe name Ornite N10. The function of this agent is to couple the othertwo surface active agents together and to aid in their balance toproduce a greater activity in the reduction of surface tensions of theoil and water encountered by the solvent in the producing formation.

The carbon bisulfide is a liquid which has a high affinity forcarbonaceous and sulfur bearing hydrocarbon materials. When used in asolvent such as xylene bottoms, it functions as a stabilizing catalystto increase the capacity of the xylene bottoms for maintaining dissolvedparafiin in solution even though such solution is cooled.

The naphthalene functions to aid in the dispersion of the paraffin anddirectly increases the penetration rate and solution rate of thesolvent.

The kerosene is used as a diluent and carrier for the combined materialsin the additive and assists in retaining dissolved paraflin in solution.

The terpene hydrocarbons are a mixture of terpene hydrocarbons,predominantly alpha pinene, dipentene and beta pinene and containsmaller percentages of terpene alcohols. The terpene hydrocarbonsfunction as an accelerator to aid in increasing the dissolving of theparaffin, particularly where very dense paraffin deposits areencountered.

While the preferred solvent composition set forth above details specificquantity relationships and materials, it is contemplated that variationsin the particular components or their equivalents which perform theindicated functions and variations in the quantities of such componentsmay The method The method of the present invention involves theintroduction of a heated solvent into a well bore to allow the solventto dissolve the parafiin from the portion of the producing formationwithin a few feet of the well bore. It has been discovered that aparatfin solvent, such as Xylene bottoms, if heated sufficiently so thatit comes into contact with the paraffin deposits at a temperature of 150F. or higher, will dissolve substantially more paraflin than the samesolvent will dissolve at lower temperatures, such as 75 F. It isbelieved that the heating of the solvent not only increases thesolubility of the solvent but also melts the paraffin deposits. Themelted paraffin is more readily taken into the solution. This heating ofthe solvent not only increases the amount of paraffin dissolvedinitially but also is believed to increase the amount of paraffin whichremains in solution after the solvent has cooled to the temperature ofthe formation. A further advantage obtained by heating the solvent isthat the solvent penetrates farther into the formation from the wellbore than would be possible with the same solvent used in an unheatedcondition. This is advantageous since paraffin deposits which occur in aproducing formation are not believed to be only at the face of theformation exposed by the well bore but in that portion of the formationwithin a few feet of the well bore. Removal of the paraffin deposit inthe formation around the exposed face allows substantial increase involume of fluids that may be produced from the well.

The method of the present invention is hereinafter described in relationto an oil well which is being pumped and which has lost productioncapacity due to paraffin deposits in the producing formation in the areasurrounding the well bore. When treatment of such well is to begin, thepump and rods are removed together with the production tubing. Suchequipment, while at the surface, is preferably cleaned and replacementparts needed are pro- The amount of solvent to be used is preselected tocompletely fill the well bore over the height of the producing formationand to move solvent out into the producing formation to a distancebetween two to five feet radially from the well bore. In actualpractice, 4,310 gallons and 2,155 gallons of solvent have been used withsuccess in treating well bores to remove paraffin.

The solvent is preferred to remain within the well bore in contact withthe producing formation for a period cured. With the well bore clear'ofproduction equipment,

it is cleaned, as by bailing. Thereafter, the production tubing islowered into the well bore. The tubing is hung in the well bore withcare being taken, if the lower end of the tubing is normally near thebottom of the well bore, to assure that its lower end is positionedsufficiently above the bottom of the well bore to allow for thermalexpansion.

- In other words, suflicient heat must be provided to allow for the heatloss of the solvent during its passage through the production tubing tothe producing formation. It has been found in practice that heating thesolvent to a temperature of 300 F. has resulted in the solvent having atemperature in the well bore at the producing formation of 225 F. Suchpreselected temperature must also take into account the effect it willhave on the solvent, i.e.,

it should not be sufiicient to vaporize substantial quantities.

of the components of the solvent.

of time sufficient for it to dissolve substantially all of pump rods cantake sufficient time for an adequate action of the solvent beforepumping from the well bore is commenced. In practice, the solvent whichhas remained in the well bore from two to twelve hours has providedexcellent increases in production capacity.

The pumping from the well is started when the solvent has been in thewell bore for the desired length of time. Initially the well productionis primarily solvent having paraflin in solution and thereafter fluidsfrom the producing formation are pumped from the well bore.

This method of treating a well to remove paraffin de posits has beenfound to be very successful. In one well, treated as described with4,310 gallons of solvent, the oil production was increased from eightbarrels per day to fifty-one barrels per day, which increased productionhas been maintained for a period of sixty days after the treatment.Another well treated according to the method of the present inventionwith 2,155 gallons of solvent, experienced an increase in oil productionfrom thirteen barrels per day to sixty-six barrels per day. Theincreased production achieved by treatment of these two wells is a verysignificant increase which is unexpected in the light of other methodspreviously used for treating wells. Another factor noticed in theproduction from treated wells is that other fluids, such as water, areproduced in increased quantities which along with the increased oilproduction is believed to establish that not only are the paraffindeposits removed from the exposed face of the producing formation in thewell bore but the paraffin deposits are removed from the formation in anarea surrounding the well bore.

The initial production from the well immediately after treatment is thesolvent which has remained in the well bore. Consideration should begiven to separating the initial production in a volume which may be aslarge as half of the solvent injected into the well bore. Since it maycontain only a minimal amount of dissolved paraffin, this solvent, ifseparated, may be suitable for re-use when reheated in combination withfresh solvent. This re-use of a portion of the solvent reduces the costof treating the well. The remaining solvent pumped from the well isdelivered to the usual storage tank and may be sold with the oil withwhich it is commingled. The price of oil as produced is less than theprice of the solvent but the solvent can readily be sold with the oil.This further reduces the cost of the well treating.

From the foregoing, it can be seen that the present invention providesan improved method of removing paraflin' from an oil well to achievesubstantial increases in oil production at a reasonable cost by removingparafiin both from the exposed face of the formation and from that partof the formation outwardly around the well bore. Also, the preferredsolvent of the present invention has a greatly improved capacity forretaining dissolved paraffin in solution by virtue of the stabilizingcatalyst additive which also accelerates the dissolving of the paralfindeposits and facilitates the entry of the solvent into the producingformation.

What is claimed is: r

1. The method of removing paraffin deposits from the producing formationsurrounding the exposed face thereof in a well in which the normaltemperature of such formation is less than F. including the steps ofheating an amount of a xylene bottoms paraflin solvent to a preselectedtemperature, a

said amount of solvent being sufficient to fill the well bore over theheight of the producing formation and to fill the formation outwardly atleast two feet from the exposed face in the well bore,

injecting the heated solvent into the well bore to deliver the solventto the fact of the producing formation exposed in the well bore,

said preselected temperature of said solvent being sufficiently high sothat the temperature of the solvent when delivered to the face of theproducing formation is at least 150 F., and

pumping fluids from the well which fluids include the solvent anddissolved paraffin.

2. The method according to claim 1, wherein said preselected temperatureof said solvent is at least 3. The method according to claim 1, whereinsaid solvent includes a stabilizing catalyst additive comprising carbondisulfide whereby substantial amounts of paraffin dissolved thereinremain in solution when said solvent cools to formation temperature.

4. The method according to claim 1, wherein said solvent includes astabilizing catalyst additive comprising carbon disulfide andnaphthalene whereby substantial amounts of paraffin dissolved thereinremain in solution when said solvent cools to formation temperature.

5. The method according to claim 1, wherein said solvent includes astabilizing catalyst additive comprising carbon disulfide, naphthaleneand a surface active agent whereby substantial amounts of paraffindissolved therein remain in solution when said solvent cools toformation temperature.

6. The method according to claim 1, wherein said solvent includes astabilizing catalyst additive comprising carbon bisulfide, naphthalene,an oil soluble surface active agent, a water soluble surface activeagent, and a combined oil and water soluble surface active agent wherebysubstantial amounts of paraffin dissolved therein remain in solutionwhen said solvent cools to formation temperature.

7. The method according to claim 1, wherein said solvent includes astabilizing catalyst additive comprising carbon bisulfide, naphthalene,sorbitan partial fatty esters, a polyoxyethylene alkyl aryl ether, analkyl phenol ethylene oxide condensate, and

terpene hydrocarbons whereby substantial amounts 0t paraffin dissolvedtherein remain in solution when said solvent cools to formationtemperature.

8. The method of removing paraffin deposits from the producing formationsurrounding the exposed face thereof in a well in which the normaltemperature of such formation is less than 150 F. including the steps ofinitially removing the production tubing from the well bore,

cleaning the well bore,

heating an amount of a xylene bottoms paraffin solvent to a preselectedtemperature,

said amount of solvent being sufficient to fill the well bore over theheight of the producing formation and to fill the formation outwardly atleast two feet from the exposed face in the well bore,

injecting the heated solvent into the well bore to deliver the solventto the face of the producing formation exposed in the well bore,

said preselected temperature of said solvent being suffi ciently high sothat the temperature of the solvent when delivered to the face of theproducing formation is at least 150 F., and

pumping fluids from the well which fluids include the solvent anddissolved paraffin.

References Cited UNITED STATES PATENTS 411,478 9/ 1889 Waldstein.1,844,883 2/1932 De Groote. 2,223,141 11/1940 Vobach. 2,339,096 1/1944-Morgan. 2,753,939 7/1956 Carpenter et al. 2,836,659 5/1958 Bock et al.2,927,078 3/1960 Nathan. 3,051,653 8/1962 Skolaut et al. 3,076,757 2/1963 Knox et al. 3,096,777 7/1963 Parks et al. 3,127,345 3/1964 DeGroote et al. 3,172,473 3/1965 Crowley et al. 3,241,614 3/1966 Bertness.3,276,519 10/1966 Knox et al. 3,279,541 .10/ 1966 Knox et al. 3,357,48712/1967 Gilchrist et al.

OTHER REFERENCES Reistle, C. E., Jr.: Paraffin and Congealing-OilProblems, Bureau of Mines Bulletin 348, 1932, pp. -73, 84 and 85.

CHARLES E. OCONNELL, Primary Examiner. I. A. CALVERT, AssistantExaminer.

- US. Cl. X.R. 166-304; 2528.55

